1. Field of the Invention
The present invention relates to a method for taking countermeasures against faulty molding in an injection molding machine, and more particularly, to a method which makes restoration to a nondefective molding condition, with the aid of an expert system, when faulty molding takes place during the mass production of molded products.
2. Description of the Related Art
A molding condition for carrying out an injection molding cycle includes a large number of molding parameters such as injection pressure, injection time, etc. Thus, in order to establish an optimum molding condition, optimum values of various molding parameters must be determined. The optimum molding condition also varies in dependence on the type of products. For these reasons, the optimum molding condition is generally determined in a trial-and-error manner by repeating an operation of carrying out an injection molding cycle in accordance with a tentative molding condition, and then changing the molding condition in accordance with the type of faulty molding found in the resultant molded product. Therefore, proper and quick setting of an optimum molding condition requires a skilled person having various knowledge and experiences. In this respect, an expert system, which enables an unskilled person to set the optimum molding condition, has been recently developed. The expert system, which comprises programs and a database prepared beforehand on the basis of the knowledge and experiences of skilled persons, is arranged to effect an optimum molding condition setting process on an interactive basis with an operator.
Once an optimum molding condition is established as described above, an injection molding machine repeats the injection molding cycle in accordance with the optimum molding condition thus established, to perform the mass production of molded products. During this time, in general, the injection molding cycle is implemented repeatedly under the same optimum molding condition, without changing the molding condition. Nevertheless, defective moldings are produced occasionally. In this case, a diagnosis is conducted to identify the cause of the faulty molding, and the optimum molding condition is set again in accordance with results of the diagnosis. However, the mechanism of occurrence of faulty molding is complicated, and various molding parameters are involved therein. Also, there are various types of faulty molding such as burrs, sinks, etc. In addition, similar faulty molding is not necessarily caused by similar improper molding parameters. This means that, when faulty molding takes place, the knowledge and experiences of the skilled are required to determine which ones of the many molding parameters should be changed and how much they should be changed to make restoration to a normal molding condition.
Thus, it may be considered to use the expert system to make a restoration process when faulty molding occurs during the mass production of molded products just as it is used to establish an optimum molding condition prior to the start of the mass production. However, the conventional expert system is primarily designed from a viewpoint of enabling determination of a new optimum molding condition on the basis of various molding parameter values detected as the injection molding cycle is repeatedly tried, with molding parameter values changed, and data indicative of the conformity of molded products and entered by an operator during the repetitive molding. According to the conventional expert system, therefore, it is impossible to efficiently perform a restoration process which is required upon occurrence of faulty molding during the mass production of molded products conducted under the same optimum molding condition.